The Iowas were
completed in 1943-44 in Navy yards
and
were arguably the finest battleships ever built, and certainly the best
U.S.
battleships. Design studies began in January 1938 and took full
advantage of the escalator clauses of the naval disarmament
treaties, which permitted 45,000 ton battleships armed with 16"
(406mm) guns. An additional constraint on their design was the
requirement that
they be capable of transiting the Panama
Canal. This drove the decision to use internal armor belts, since
there was little possibility of designing a ship with adequate external
belts that could fit through the Canal.

The previous North Carolinaand
South Dakota classes had been
designed to take advantage of the 16" gun escalator clause, but not the
45,000 tons displacement escalator clause. The Navy had been remarkably
successful in meeting its design goals on a 35,000 ton displacement,
particularly in the case of the South
Dakotas, which were arguably the most cost-effective battleships
ever built. In the case of the Iowas,
the question before the Navy designers was how make best use of the
extra 10,000 tons.

Two schools of thought emerged. The "slow
battleship" school argued for using the extra displacement to increase
protection and firepower even at the cost of speed. This concept was
eventually approved in the form of the Montanas, which somewhat resembled
the JapaneseYamatos,
and whose large beam anticipated plans to widen the Panama Canal.
However, the Montana program
was postponed and then canceled before any of the ships were laid down.
The other school of thought, the "fast battleship" school, argued for
using the extra displacement to increase speed and endurance, and this
concept was approved as the Iowa class.

The design process was not entirely smooth. The underwater protection system was based on that of the South Dakotas
and suffered from the same difficulty with the armored bulkhead. Once
the difficulty was discovered, the only solution was to liquid load the
outer tanks rather than the inner tanks. Another difficulty was a nearly
disastrous miscommunication which left the Bureau of Ordinance
designing turret barbettes with a diameter of 40' (12.19m) and the
Bureau of Construction and Repair designing the hull for turret
barbettes that were 39' (11.89m) in diameter. The discrepancy was
discovered too late in the design process for the hull form to be
modified to accommodate the larger barbette, and the Navy was forced to
abandon the use of the heavy but reliable Mark II gun in favor of a
new lightweight gun, the Mark 7 in a redesigned turret. Fortunately, the
Mark 7
proved to be an excellent weapon. Another late revision in design came
from a suggestion by New York Navy Yard that the four large machinery
spaces that were originally planned be broken into eight spaces, one
for each set of machinery and for each pair of boilers, at the cost of a
slight increase in beam. This gave the ship excellent subdivision and
was judged well worth the cost.

Thanks to improvements in machinery and hull form,
the Iowas were as fast as battle
cruisers, and a full full six
knots faster than the South Dakotas or their arch-rivals, the Yamatos. This made the Iowas excellent escorts for the fast carrier task forces that
dominated the Pacific War. This may seem foresighted, considering that
that the concept was approved in April 1938, but it was more a
fortuitous response to an international trend toward fast battleships
than any prescience regarding the future role of carriers.

The Iowas had nearly the same armament, armor, and underwater protection as the South Dakotas,
but were less cramped. Their armor
belts were thinner than the Yamatos,
but were better arranged and made of slightly superior alloys. The Iowa
main armament was two
inches smaller in caliber than the massive 18" guns of the Yamatos,
but had excellent ballistic performance and penetration, a higher sustained rate of
fire, and
much better fire control. The Iowas also had a
much superior antiaircraft
battery, built around radar-guided
and –fused 5”/38s and forests of 40mm and
20mm light antiaircraft guns.

Each set of machinery consisted of a high-pressure turbine
with one Curtis stage and eleven Parsons stages and a low-pressure
turbine with
six Parsons stages. The low-pressure turbine had an astern section
consisting of a single Curtis stage. Each high-pressure turbine
was supplied with steam at a pressure of 565 psi (3.90 MPa) and a
temperature of or 850 F (454 C) from two M-type boilers. The reduction
gearing for the high-pressure turbine had a reduction of 24.284:1 and
that for the low-pressure turbine had a reduction of 19.369:1. Auxiliary
power was provided by eight 1250 kW generators.

Fire control for the main battery was provided by two Mark
38 directors, each with 1.5" (38 mm) of STS splinter protection, backed
up by rangefinders in each turret. The other elements of the fire
control system were located in a plotting room in the armored citadel.
By the time the ships were completed, Mark 8 radar
had become a standard part of the Mark 38. The 5" battery was directed
by four Mark 37 directors and the 40mm battery by Mark 51 directors near
each mount. In addition to the air and surface search radars listed
above, the Iowas received SPT-1 and SPT-4 directional jammers in 1944 to foil enemy radar.

If the Iowas had a
weakness, it was their fine
lines, which rendered the bow wet and vulnerable to damage.

Though widely regarded as arch rivals, the Iowas and Yamatos never tested each other in
combat. The closest they
came was at Leyte Gulf;
but Halsey
took the Iowas north to chase the Japanese decoy
carriers, while Kurita
took the surviving Yamato south in a
vain effort to engage the American amphibious forces.

The Iowas
proved remarkably adaptable to modernization, and were brought out of
mothballs to serve in most of the serious conflicts of the last half of
the 20th century. The last two units were finally retired for good in
2006, though, since all the Iowas
became museum ships rather than being scrapped, it is barely possible
they will yet see combat again.